ST-segment elevation myocardial infarction

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Background

  • RV infarction accompanies ~25% of inferior STEMIs
    • Hemodynamically significant only 10% of the time
  • Posterior infarction is rarely isolated (~3-8% of all AMIs)
    • Usually will see changes in V6 OR II, III, aVF

Diagnosis

Use the J-point for measurement in 2 contiguous leads:[1]

  1. Men ≥ 40yo:
    1. 2mm in V2-V3 and 1mm in all other leads
  2. Men≤40yo:
    1. 2.5mm in V2-V3 and 1mm in all other leads
  3. Women:
    1. 1.5mm in V2-V3 and 1mm in all other leads

Anatomical Correlation

DDx

  1. Myocardial ischemia or infarction
  2. Noninfarction, transmural ischemia (Prinzmetal's angina pattern or acute takotsubo cardiomyopathy)
  3. Post-MI (ventricular aneurysm pattern)
  4. Previous MI with recurrent ischemia in same area
  5. Pericarditis
  6. Early repolarization
  7. LVH or LBBB (only V1-V2 or V3)
  8. Myocarditis (may look like myocardial infarction or pericarditis)
  9. Brugada Syndrome
  10. Myocardial tumor
  11. Myocardial trauma
  12. Hyperkalemia (only leads V1 and V2)
  13. Hypothermia (J wave/Osborn wave)

Treatment

Adjunctive

  1. O2
    1. esp for SpO2 <90%
  2. ASA 162-325mg chewable or 600mg PR
  3. NTG
  4. Morphine
  5. Beta-Blocker:
    1. PO within 24 hours
    2. IV beta-blocker is reasonable for patients who are hypertensive in the absence of:
      1. Heart failure
      2. Low cardiac output state
      3. Cardiogenic shock risk factors
        1. Age > 70yr, sys BP < 120, HR > 110 or <60,
      4. Conduction block (PR interval > 0.24s, 2nd or 3rd block
      5. Active asthma

Antiplatelets

  1. Clopidogrel
    1. Loading dose
      1. 600mg if PCI anticipated (otherwise give 300mg)
      2. No loading dose if >75yr receiving fibrinolytics
  2. GPIIB/IIIa Inhibitors (Abciximab, Eptifibatide)
    1. Defer to cardiologist
    2. Given right before PCI

Anticoagulation

  1. Heparin (UFH)
    1. Bolus 60U/kg (max: 4000U) followed by 12U/kg/h (max: 1000U/h)
    2. Titrate to PTT 1.5-2.5 x control
  2. LMWH
    1. <75yo with serum Cr < 2.5 mg/dL (men) or < 2.0 mg/dL (women):
      1. 30mg IV bolus followed by 1mg/kg SC q12h
    2. ≥ 75yo
      1. 0.75mg/kg SC q12h
    3. CrCl < 30 mL/min
      1. 1mg/kg SC qd
  3. Fondaparinux
    1. Cr < 3.0 mg/dL:
      1. 2.5mg IV bolus then 2.5mg SC qd started 24hr after bolus
    2. Monitor anti-Xa levels
  4. Bivalirudin
    1. 0.75mg/kg IV bolus followed by 1.75 mg/kg/h
    2. CrCl < 30 mL/min
      1. 0.75mg/kg IV bolus followed by 1.0 mg/kg/h

Definitive

  1. Fibrinolytics
    1. Goal: Give within 30min
    2. If receive fibrinolytics also give anticoagulants for minimum of 48hr
    3. Fibrinolytic tx w/in 3hr resulted in >30 lives saved per 1000 pts
    4. 0.5-1% of pts suffer ICH
  2. PCI
    1. Goal: Give within 90min (acceptable delay may be up to 120min)

Fibrinolysis

Indications

  1. <12hr from onset of CP AND:
    1. ST elevation of ≥1mm in 2 contiguous limb or precordial leads OR new LBBB

Contraindications

  1. Absolute contraindications
    1. Any prior ICH
    2. Known structural cerebral vascular lesion (AVM)
    3. Known intracranial neoplasm
    4. Ischemic stroke w/in 3 mo
    5. Active internal bleeding (excluding menses)
    6. Suspected aortic dissection or pericarditis
  2. Relative contraindications
    1. Severe uncontrolled BP (>180/100)
    2. History of chronic severe poorly controlled HTN
    3. History of prior ischemic stroke >3 mo
    4. Known intracranial pathology not covered in absolute contraindications
    5. Current use of anticoagulants with known INR >2–3
    6. Known bleeding diathesis
    7. Recent trauma (past 2 wk)
    8. Prolonged CPR (>10 min)
    9. Major surgery (<3 wk)
    10. Noncompressible vascular punctures (e.g. IJ, subclavian)
    11. Recent internal bleeding (within 2–4 wk)
    12. Pts treated previously with streptokinase should not receive streptokinase a 2nd time
    13. Pregnancy
    14. Active peptic ulcer disease
    15. Other medical conditions likely to increase risk of bleeding (diabetic retinopathy, etc)

Dosing (Alteplase)

  • >67kg pt:
    • Infuse 15mg IV over 1-2min; then 50mg over 30min; then 35mg over next 60min (i.e. 100mg over 1.5hr)
  • ≤67kg pt:
    • Infuse 15mg IV over 1-2min; then 0.75 mg/kg (max 50mg) over 30 min; then 0.5 mg/kg over 60min (max 35 mg)

Dosing (Tenecteplase-TNKase)

  • Reconstitute 50 mg vial in 10 mL sterile water (5 mg/mL)
  • < 60 kg = 30 mg IV push over 5 seconds
  • 60-69 kg = 35 mg IV push over 5 seconds
  • 70-79 kg = 40 mg IV push over 5 seconds
  • 80-89 kg = 45 mg IV push over 5 seconds
  • > 90 kg = 50 mg IV push over 5 seconds

Rescue PCI

  • Failed reperfusion: consider if repeat EKG 90 minutes after infusion fails to show reduction of elevated ST segments by 50%
  • Recurrent significant ST elevation following successful lysis
  • Persistent hemodynamically unstable arrythmias, persistent ischemic symptoms, or worsened cardiogenic shock

See Also

Source

  • ACC/AHA Practice Guidelines 2004/5
  • EBM 6/09
  • Electrocardiography in Emergency Medicine. ACEP Textbook
  1. ↑ Thygesen, K., Alpert, J. S., Jaffe, A. S., Simoons, M. L., Chaitman, B. R., White, H. D., et al. (2012). Third Universal Definition of Myocardial Infarction. JACC, 60(16), 1581–1598. doi:10.1016/j.jacc.2012.08.001
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